This coming year we plan to develop an indirect quantitative radioimmunoassay for the analysis of myelin membranes from 9 sub-subfractions of central nervous system rat brain myelin. The assay will need to encompass syngeneic Lewis-rat-anti-Lewis-rat-myelin antibodies for which we will use a rabbit-anti-rat-immunoglobulin-light-chain IgG (already raised and evaluated). This is necessitated by our observations that rat antimyelin antibodies are frequently distributed among several of the 7 main classes of rat immunoglobulins; in order to capture all relevant myelin-binding activity we must be prepared to encounter any and all classes. Subsequent to this general indirect radioimmunoassay, specific indirect radioimmunoassays involving antibodies to specific classes of rat immunoglobulins will be used to measure the distribution of antimyelin activity in the syngeneic system. An indirect RIA for the quantitative measurement of antibody binding to neuroectodermal cells in monolayer culture has already been developed, and will be used to continue to explore the surface antigens of glial cells, except that now allogeneic and syngeneic as well as xenogeneic systems will be involved. In order to accomplish all these goals we will need to separate, identify, and raise antibodies against the various rat immunoglobulin classes, a project that is well underway with separation and identification nearly complete and with some antisera already raised. BIBLIOGRAPHIC REFERENCES: Harwood, S.E., Bigner, D.D., Wechsler, W., and Day, E.D., Sequential adsorption analysis of antibodies to neuroectodermal cells by an indirect quantitative method, J. National Cancer Inst., in press, 1976. Pitts, O.M., Varitek, V.A., and Day, E.D., The extensive cross-reaction of syngeneic rat-anti-BP serums with other BP's, Immunochem. 13:in press, 1976.